[msarnoff]

Assuming you have physical access to the inside of the machine…

Most all machines from the 80s and 90s (Williams/Bally/Gottlieb) store their high scores and adjustments in an SRAM like a 5101 with a battery backup. They are stored in binary-coded decimal and protected by a checksum.

If you could tap into the bus (possibly while the CPU is halted or by removing it) you could modify its contents.

A common aftermarket mod is to remove the backup battery (they like to corrode) and replace the CMOS RAM with a nonvolatile FeRAM. In that case, just pop it into a programmer like a TL866 and program a new image with your desired high scores.

I’ve considered doing this… I wish my 1.2 billion on my Getaway hadn’t been wiped out…